The invention relates to an indexable insert milling tool.
From DE 43 04 071 there is known a plane cutter with indexable inserts in which the milling indexable inserts are arranged in insert seats which are formed in the chip spaces of the milling body. The insert seat and the milling indexable insert are arranged such that a negative radial angle of the insert seat, a negative axial angle of the insert seat and a positive effective cutting angle are in each case 12.degree. to 18.degree., preferably 15.degree.. Inspite of the large effective cutting angle for the indexable inserts there results a stable cross section since the lateral surfaces (free surfaces) may run at right angles to the bearing surface. The chip spaces are relatively short. They may therefore be worked in with relatively short milling tools which keeps the manufacturing cost small. The geometry of the chip spaces furthermore permits a smaller separation of the plane miller, i.e. a higher cutting speed. Finally the bores on the tool holder for fastening the indexable inserts may be designed relatively long. By way of this the security of the insert seat is increased even further.
With high speed millers the fastening of indexable inserts is loaded very heavily. With this there exists the danger that the high centrifugal forces loosens screw fastenings or lead to the shearing off of the tensioning screws. Independent of this a fastening of the indexable insert is very heavily loaded by way of the cutting forces, above all with a negative mounting angle.
It is therefore the object of the invention to provide an indexable insert milling tool in which the indexable inserts are arranged and fastened in the milling body such that they are able to resist high cutting and centrifugal forces.
With the miller according to the invention the indexable insert on the rear side on the cutting edge side comprises a raised elongate support section wedge-shaped in cross section with a lower support surface, wherein the distanced support surfaces run parallel on the rear side of the indexable insert. In the insert seat bordering the bearing surface which assumes the radial loading and against which therefore the lateral surface of the indexable insert bears there is formed a recess with surfaces approximately parallel to the second bearing surface. The recess in cross section is formed complementarily to the cross section of the support sections in a manner such that the support section is accommodated in the recess with an approximately positive fit and the indexable insert on tightening the fastening screw on account of the wedging effect is pressed against the second bearing surface whilst the support surface of the other support section bears against a radial outer section of the first bearing surface.
In other words, the radial bearing surface together with a wedge surface of the recess forms the possibility of a positive-fit connection to the complementarily formed support section. As a result of the wedging effect on tightening the fastening screw a force component against the radial bearing surface is produced. By way of this the indexable insert on the carrier body is centered and is effectively secured against a drifting to the outside.
The rear-side support surface of the respective other support surface at the same time lies on the first bearing surface of the miller body. The indexable insert therefore has a bridge-like cross section on the rear side. The indexable insert is therefore relatively broadly supported.
The design according to the invention has several advantages. The indexable insert may be arranged at a relatively large negative mounting angle. By way of this there results a favourable chip space with a relatively small volume which permits a narrow tooth pitch angle to be achieved, i.e. a large cutting number on the circumference of the miller. At the same time it is prevented that the indexable insert is pulled out by way of cutting forces.
In spite of a narrow tooth pitch comparatively stable indexable insert cross sections with large positive free angles and effective cutting angles may be applied.
A further advantage is the good workability of the insert seats (with a large negative mounting angle). Relatively short and stable working tools with low unclamping lengths may be applied.
The centering effect of the described clamping system ensures that the indexable inserts compellingly are clamped with a high truth of running. A twisting of the indexable insert or a radial displacement is ruled out, and specifically during the clamping procedure as well as cutting loading on application. Apart from the increased clamping security as a side effect there arises advantages on reversing or changing the indexable insert. With the clamping procedure the indexable insert is only yet to be displaced in the axial direction against the bearing of the insert seat.
The main advantage of the design according to the invention is however the great strength of the seat of the indexable insert with respect to attacking cutting forces and high centrifugal forces.
The radial bearing surface in the recess on the one hand and the radial bearing surface for the lateral walling of the indexable insert on the other hand may be formed by differing surfaces. According to one formation of the invention it is however advantageous when the second bearing surface forms a wall of the recess.
As already mentioned the back of the indexable insert in cross section is preferably trapezoidal. The insert seat may on the first bearing surface which faces the rear side comprise a rectangular base in the form of a pyramid base which is formed around the threaded bore and whose wall directed towards the second bearing surface represents the wall of the recess forming the wedge surface.
Corresponding to the above embodiment form the rear side of the indexable insert may be formed as a rectangular frame of which two oppositely lying sides form the support section and comprise the support surfaces. The frames connect the support sections to one another and thus stabilize the indexable insert against undesirable deformation.
According to a further formation of the invention the chip space comprises an axial third bearing surface against which one end-face side of the indexable insert comes to bear. Such a bearing surface is however known per se with indexable insert seats in milling bodies.
According to a further formation of the invention the axis of the threaded bore is arranged such that the fastening screw presses the indexable insert against the third bearing surface. By way of this the indexable insert is pretensioned against the third bearing surface.
The indexable insert is mounted in the milling body preferably with a relatively large positive axial angle, the free surface of the indexable insert of the main cutting edge according to another formation of the invention is preferably crowned. The face is according to another formation of the invention designed in the form of a flute.
According to a further formation of the invention the indexable insert at the end-face side may comprise a minor cutting edge with a flanging radius and a plane bezel.